Brass Adapter, 3/8-18 Male NPT To 1/2-20 Male SAE 45 deg Flare, 90 deg Elbow

That's what this adapter is built for. One end threads into your 3/8-18 NPT male port, and the other end connects to a 1/2-20 male SAE 45 degree flare. The 90 degree elbow body handles the direction change, so you're not fighting the line trying to make a hard bend somewhere downstream. It's brass construction, so it's a solid fit for most fluid system work where you need a clean right-angle transition between those two thread types.